1. Field of the Invention
This invention relates to a light exposure method for ultra-fine processing in the field of a semiconductor.
2. Description of Related Art
In, for example, the field of a semiconductor, establishment of a new processing technique providing for ultra-fine processing to a size not larger than 0.1 xcexcm is incumbent with the tendency towards high integration semiconductor devices.
In processing an ultra-fine pattern, the so-called lithographic technique is indispensable. At present, development of a new light exposure technique employing an extreme ultraviolet (EUV) rays in the vicinity of the wavelength of 7 to 16 nm, in addition to the ultraviolet rays by a conventional mercury lamp or excimer laser, is going on briskly in order to improve optical resolution to cope with shorter wavelengths used for light exposure to achieve the ultra-fine processing.
However, the wavelength range of the extreme ultraviolet (EUV) suffers a problem that, with the wavelength range of the ultraviolet (EUV), usual resist materials undergo significant optical absorption, such that the illuminated light cannot reach the deeper portion in the resist layer to deteriorate the resist pattern.
This deterioration in the resist pattern hampers ultra-fine processing and, hence, it is desirable to improve the ultra-fine processing.
It is therefore an object of the present invention to eliminate the aforementioned problem and to provide a light exposure method in which the problem pertinent to light transmittance of a resist layer in the wavelength range of the extreme ultraviolet (EUV) may be eliminated to enable more elaborate ultra-fine processing.
According to the present invention, there is provided a light-exposure method in which a resist layer is exposed selectively to X-rays, vacuum ultraviolet rays, extreme ultraviolet rays or soft X-rays to pattern the resist layer to a pre-set shape, wherein, as a high molecular material of the resist layer, a high molecular material is obtained on replacing at least a portion of hydrogen atoms of a pre-existing resist material by a substituent containing an alkyl group and/or a substituent containing an aromatic ring.
The resist material herein means the totality of resist materials known prior to filing of the present application.
Usually, in the high molecular materials constituting the resist layer, the presence of oxygen atoms is indispensable for displaying resist characteristics. In high molecular materials, the portions subjected to a certain chemical reaction due to light illuminated thereon to produce changes in the physical values of the illuminated and non-illuminated portions to demonstrate resist characteristics are groups necessarily containing oxygen, such as ester, phenolic, alcoholic or carboxylic groups.
In the wavelength range of the extreme ultraviolet (EUV) light, optical absorption of oxygen is larger than that of carbon or hydrogen, and is responsible for lowering of the light transmittance of the high molecular materials. The optical absorption per oxygen atom is as large as approximately thrice that of carbon atoms, and approximately 50 to 100 times that of the hydrogen atoms.
According to the present invention, in which hydrogen atoms in the pre-existing resist material are replaced by substituents containing alkyl groups or substituents containing aromatic rings, the proportion of oxygen atoms in the atoms making up the high molecular materials is relatively small to suppress the optical absorption of the high molecular material in its entirety.
According to the present invention, in which a high molecular materials having an alkyl group or an aromatic ring introduced therein to raise the light transmittance in the wavelength range of the extreme ultraviolet rays is used as a resist material, a resist pattern of a desirable shape may be produced to enable ultra-fine processing more elaborate than is possible with the conventional method.
Moreover, in an extreme ultraviolet (EUV) lithographic process, the film thickness of the resist layer can be increased by employing a high molecular material exhibiting high transparency, thereby improving resistance to etching of the resist layer.